This invention relates, in general, to semiconductor lasers, including, but not limited to, vertical cavity surface emitting lasers (VCSELs).
Semiconductor lasers are important for use as optical devices. In the past, edge emitting devices, in which the output light is emitted parallel to the semiconductor substrate, have been fabricated. However, vertical cavity devices, in which the output light is emitted perpendicular to the semiconductor substrate, are much more advantageous in certain applications. Vertical cavity devices have advantages such as high two-dimensional packing density for arrays and integrated circuits, wafer scale testing ability, and can be readily integrated with other devices. Although much research and improvement has been done on VCSELs, there is still a need to fabricate more efficient lateral injection VCSELs for optical interconnect applications and displays.
A VCSEL used in the past is a mesa-etched device. These mesa-etched VCSELs are limited to small spot sizes, resulting in devices having low output power and high series and thermal resistances. Therefore, there is a need to form more efficient VCSELs with high power output and low series and thermal resistances. Another disadvantage of mesa-etched devices is that they are highly non-planar and it is difficult to take the light output out of the top of the device. Planar structures are desirable from a process and packaging point of view.
A way of fabricating planar VCSELs has been disclosed by Hasnain et al, in Electronics Letters, Vol. 26, No. 19, pp. 1590-91, published on Sep. 13, 1990. These VCSELs are proton bombarded to provide for lateral current confinement. These devices, however, have potential problems with reliability and with thermal waveguiding. Thermal waveguiding is disadvantageous because the optical properties of the device can change when the device heats up. In addition, the output beam of these devices is not diffraction limited due to the fact that waveguiding is provided only by the injected current distribution and the junction temperature distribution.